1. Field of the Invention
The present invention relates to a camera having a real focal length photographing mode (normal mode) for printing a normal photographing range on a photographic paper and a pseudo focal length photographing mode (trimming mode) for printing in a narrower range of field and effecting a film printing at an enlarging ratio different from a normal enlarging ratio in printing to obtain a print as if it had been photographed by a telephoto lens.
2. Description of Related Art
In photographing, it is important to decide a composition to be reproduced on a photographic paper. To this end, there is known a method in which the distance up to an object to be photographed is changed or photographing is performed using an interchangeable lens or a zoom lens, and a method in which a film is checked after photographing and a decision of composition to be reproduced is made by trimming.
As a camera based on the method utilizing trimming there has been proposed a camera in U.S. Pat. No. 3,490,844 and Japanese Patent Application Laid-open Publication No. 54-26721 (26721/79) in which a finder optical system capable of changing the size of field indicated therein is provided in the camera to thereby select an image frame range to be photographed, and a trimming information is recorded on a film in interlock with the finder optical system, while in printing, a part of the photographed image frame is printed at an enlarging ratio different from a normal enlarging ratio on the basis of the trimming information, whereby there can be obtained a print as if it had been photographed by a telephoto lens having a focal length larger than that of the lens originally attached to the camera.
When a photograph taken from an object in such pseudo focal length photographing mode is compared with a photograph taken from the same object but using a lens having a focal length equal to that which has been set in a pseudo manner by the pseudo focal length photographing mode, it is seen that the depth of field is larger in the former by the trimming proportion than in the latter.
If the distance up to an object is U (provided U.gtoreq.f) and F-number of a lens is F, and the diameter of an allowable circle of confusion is .delta., then a depth of field a.sub.1 of a lens having a focal length f=f.sub.1 is represented as follows: ##EQU1## Likewise, a depth of field a.sub.2 of a lens having a focal length f=f.sub.2 is represented as follows: ##EQU2##
On the other hand, in the where a photograph taken by the lens of focal length f=f.sub.1 is subjected to trimming so that it corresponds to a photograph taken by the lens of focal length f=f.sub.2, the diameter of a confusion circle corresponding to f=f.sub.2 must be .delta., so the diameter of a confusion circle at f=f.sub.1 bcomes .delta..times.f.sub.1 /f.sub.2. A depth of field a.sub.3 at this time is represented as follows: ##EQU3##
Therefore, if a comparison is made between the depth of field a.sub.3 obtained after trimming of the photograph taken by the lens of focal length f=f.sub.1 and the depth of field a.sub.2 of the photograph taken by the lens of focal length f=f.sub.2, there is obtained the following result: ##EQU4## Thus, the depth of field is larger f.sub.2 /f.sub.1 times in the adoption of trimming and this magnification corresponds to the proportion of trimming, so the depth of field becomes larger by an amount corresponding to the proportion of trimming.
As a result, in the case of a print obtained from photographing in a pseudo focal length photographing mode, the probability of both a main object and surrounding objects entering the depth of field increases and the resulting photograph is in focus to both the main object and the surrounding objects, making it difficult to make a clear distinction of the two. Consequently, the photograph is confused and unsightly.
Further, when a color photograph of a person is taken using a flash light emitting device in a dark place, the person's eye is sometimes photographed as a red eye, and this phenomenon is called a red-eye phenomenon. Although this phenomenon has not been made clear completely, it is said that the light emitted from the flash light emitting device is reflected by the choroid located behind the retina in the interior of the human's eyeball and this reflected light causes the pupil to be photographed red.
This red-eye phenomenon is apt to occur when the distance between the photographing lens of the camera and the flash light emitting device is short or as the photographing distance between the photographing lens of the camera and the eye of person to be photographed.
As a solution to this problem there has been proposed a camera constructed so that the sufficient distance between the flash light emitting device and an optical axis of the photographing lens can be maintained constant (see Japanese Patent Publication No. 58-20021 (20021/83)).
In the photographing with a camera having a pseudo focal length photographing mode, a part of a photographed image frame is enlarged and even a remote object is printed large as if it had been photographed using a telephoto lens, so that there inevitably is a tendency to photographing a remote object as compared with the real focal length photographing mode, and the red-eye phenomenon is apt to occur as previously explained.
In the case of a photograph which has been taken in the real focal length photographing mode, even in the event the red-eye phenomenon should occur, it will not be so conspicuous because the enlarging ratio in printing is low. On the other hand, in the case of a photograph which has been taken in the pseudo focal length photographing mode, if the red-eye phenomenon should occur, it will be conspicuous because the enlarging ratio in printing is high.